The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2000-044100, filed on Feb. 22, 2000, the contents of which is herein expressly incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of inspecting batteries for a short circuit and to a method of manufacturing batteries.
2. Description of Related Art
Batteries including a number of positive electrodes and negative electrodes with intervening separator therebetween are subject to inspection for a short-circuit failure. FIG. 3 illustrates a prior art arrangement for one such inspection method for batteries. In the drawing, reference numeral 21 denotes an electrode plate group composed of a plurality of positive electrodes 22 and a plurality of negative electrodes 23 laminated upon one another with separators 24 interposed therebetween. The electrode plate group 21 is housed within a battery case 25. An insulation resistance tester 27 is connected across the battery case 25 with which the negative electrodes 23 are in contact and a positive electrode terminal 26 connected to one of the positive electrode plates 22 in the middle. The presence or absence of short circuit is thus determined by measuring the insulation resistance across the opposite electrode terminals.
Another example disclosed, for example, in Japanese Laid-open Patent Application No. 4-138674 is an inspection apparatus connected to a pair of pushing bars for inserting an electrode plate group into a battery case, in which voltage is applied across the pair of pushing bars during or immediately after insertion of the electrode plate group into the battery case.
Yet another example disclosed, for example, in Japanese Laid-open Patent Application No. 11-40210 involves applying high voltage across the positive and negative electrodes of an electrode plate group housed within a battery case, prior to injection of electrolyte. The electrode plate group is thus inspected for short circuits by detecting a voltage drop due to short-circuiting current. By this method, it is also possible to identify the regions where there is a risk of light short-circuiting.
The method illustrated in FIG. 3, wherein the insulation resistance of the electrode plate group 21 is measured in a state where the electrode plate group 21 is housed inside a battery case 25, had the following problem. After the battery has been charged and discharged, swelling occurs in the electrode plates, whilst the electrode plate group 21 is constrained by the battery case 25, and therefore the separators 24 interposed between the electrode plates 22, 23 are compressed by the electrode plates 22, 23. As a result, there was the risk that short-circuiting occurs after charging and discharging of the battery, due to conductive foreign matters which existed between the electrode plates 22, 23 and the separators 24, or due to burrs on the electrode plates 22, 23 which may pierce through the separators 24. Consequently, it is often the case that a battery, which has been determined as satisfactory by the inspection prior to injection of electrolyte into the battery case, will produce short circuit faults after charging and discharging of the battery.
To solve this problem, batteries are subject to aging after initial charging and discharging, so as to detect and eliminate defective products. However, this requires a long time for inspection and also high costs, since the entire process for inspection including aging with respect to defective products which are included in the complete batteries is a complete waste.
Another problem with the method wherein insulation resistance is measured is that it is susceptible to the effects of ambient humidity, resulting in false judgements regarding the presence of short circuits. The method is therefore hardly applicable to the short-circuiting inspection for batteries having a high output design.
With the inspection method disclosed in Japanese Laid-open Patent Application No. 4-138674, productivity is improved by performing inspection simultaneously with the process step for inserting electrode plate groups into battery cases. However, the method provides no solution to the above-mentioned problem that some of the complete batteries turn out to be defective later due to swelling of electrode plates. The inspection method disclosed in Japanese Laid-open Patent Application No. 11-40210 has an advantage that even the regions which are likely to produce light short circuits after a while can be identified, but it gives no assurance that no short-circuiting occurs after the complete battery undergoes charging and discharging.
With the foregoing problems of the prior art in view, it is an object of the present invention to provide a battery inspection method, whereby a battery in which short-circuiting may occur after charging and discharging of the battery due to swelling of electrode plates is detected without failure, and a battery manufacturing method wherein such inspection method is incorporated.
The present invention is a method of inspecting batteries for a short-circuiting failure, including the steps of:
laminating a plurality of positive electrode plates and a plurality of negative electrode plates alternately with intervening separators therebetween for constituting an electrode plate group; and
compressing the electrode plate group while inspecting the battery for a short circuit, prior to insertion of the electrode plate group into a battery case.
Electrode plates are compressed during the short-circuiting inspection, so as to simulate a state wherein the separators are compressed by swelling of the electrode plates after charging and discharging of batteries. Accordingly, although the inspection is performed prior to insertion of the electrode plates into the battery case, it is possible to detect a battery in which a short circuit may occur due to swelling of the electrode plates after charging and discharging of the battery.
The positive and negative electrode plates and separators may be vacuum dried before being assembled into the electrode plate group, so that the inspection is performed without being affected by ambient humidity.
The electrode plate group is compressed with such an amount of pressure that the separators are compressed to a dimension equal to a dimension to which the separators would be compressed after a predetermined number of cycles of charge and discharge of the battery. In this way, it is possible to remove batteries which may turn out to be defective after a while due to swelling of electrode plates, and reliability of the inspection is improved.
The battery is inspected for a short circuit by applying a predetermined voltage across the plurality of positive electrode plates and the plurality of negative electrode plates and by measuring electric current passing thereacross. In this way, potential causes of short circuit, such as minute foreign matters, burrs, or the like, are detected, and hence high reliability of inspection is achieved.
The voltage applied across the plurality of positive electrode plates and the plurality of negative electrode plates is set to a value that is lower than ⅔ of a threshold voltage of the compressed separators. In this way, inspection is strictly performed without causing damage to the electrode plate groups.
The present invention also provides a method of manufacturing batteries, including the steps of:
laminating a plurality of positive electrode plates and a plurality of negative electrode plates alternately with intervening separators therebetween for constituting an electrode plate group;
compressing the electrode plate group while inspecting the battery for a short circuit;
inserting an electrode plate group that has passed the inspection in the previous step into a battery case;
injecting electrolyte into the battery case; and
sealing the battery.
The manufacturing method of the invention includes the battery inspection method described above, which is performed prior to insertion of the electrode plate group into the battery case, whereby a battery in which short-circuiting is likely to occur due to swelling of electrode plates after charging and discharging of the battery is detected and removed. Accordingly, the method enables production of reliable batteries with high efficiency.
The manufacturing method may further include a step of vacuum-drying the positive and negative electrode plates and separators before they are assembled into the electrode plate group. In this way, inspection of the battery is performed without being affected by ambient humidity.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.